Alright ,theres really nothing wrong with a properly installed piercing valve.
It suffers from most of the same issues as most smaller valves.
1-It needs to be turned on/off once in a while to keep it from getting stuck and clogging up.
2-when they do leak its normally caused by the packing nut under the handle getting seized to the stem from non use.
So when you turn one on or off that hasnt been used in a long time the packing nut ends up loosening when you open the valve,you can just snug up the packing nut while holding the handle most of the time.
The other common option is to cut a 3/4x3/4x1/2 tee in there and sweat a threaded bung fitting into the 1/2" side and thread a valve into it.
Either way you should open/close the valve a couple times a year to keep it from seizing up
"facts" have no relevance to this discusion
Posting from a concrete bunker under a non descript barn